XYZ XYZ\,XYZ is a triangle. ZBAC ZBAC\,ZBAC is a parallelogram such that A A\,A is the midpoint of XYXYXY, B B\,B is the midpoint of XZXZXZ, and C C\,C is the midpoint of YZYZYZ.
Prove that triangle XAB XAB\,XAB is congruent to triangle AYCAYCAYC.